Excellent question! As I think about it I believe the First Age would be the best of tales: the finest in ‘Men’ uniting with the supernatural nature of Elves to fight the dominance of evil.
A dozen feature-length films might put a dent in the 1st Age! ^-^
IMO to do it up right a CGI digest of the his Creation mythos is a must but where that first film ends I’m not certain. The awakening of the Eleven race and some early conflicts with Morgoth...I dont recall the details!
If you don't have The Silmarillion you might consider obtaining it. It starts with the primeval world of creation and progresses through the Noldorin rebellion, the First Age, Numenor and on to the Third Age.
There are a number of progressive formative volumes such as the two volumes The Lost Tales; also the whole The History of Middle-earth series. A veritable mountain of developing Middle Earth reality.